1. Field of the Invention
The present invention relates to a method for manufacturing an aluminum electrode using a solution process and an aluminum electrode using the same.
2. Description of the Related Art
Aluminum with a low work function is generally used as a material for a cathode of an environmental energy device requiring ohmic contact, such as solar cells and OLEDs.
Due to rapid oxidization characteristic, aluminum electrodes, used as a material for a cathode of organic solar cells and OLED devices, are manufactured using thermal evaporation and sputter coating in a vacuum.
The thermal evaporation is a method in which a crucible formed of ceramic is heated by using electric heat and a material is evaporated to the crucible to form a film. Generally, a point source with a high temperature may be used for evaporating metal electrodes such as Mg—Al, Al—Li, and Al, with electric heat. In order to form a metal cathode, there is required a temperature of 1300° C., whose efficiency of using a material is 30% or less. A processing condition described above causes excessive loss of raw material and a deterioration of organics, and aluminum with a high-temperature, on a wall of a ceramic crucible, creeps over the crucible due to a great wetting angle between aluminum and ceramic, thereby reducing a replacement cycle and increasing cost of maintaining equipment.
Also, sputter coating is a method in which electrons generated by applying a negative bias to a sputter gun in a vacuum system disassociate an inactive gas and generate plasma and ion particles with high energy generated thereby collide with a surface of a target where ion particles are to be evaporated to and exchange kinetic energy in such a way that atoms or molecules bounce out of the surface and are absorbed onto a substrate. The sputter coating has a problem in which collision of particles with energy generates defects and forms local trap sites, thereby causing a structural organic distortion of an organic film. Also, the collision elevates a temperature of the surface and deteriorates properties of an organic layer.
To solve problems as described above, Plasma Process. Polym. 2009, 6, S808 discloses a method for reducing a defect of an organic layer by adjusting a voltage applied to a DC magnetron. Also, in Applied Physics Letters 88, 083513 (2006) and J. KIEEME Vol. 85, No. 19, 8 (2004), a defect of an organic layer is prevented by using a mixture gas of Ar and Kr for sputtering. However, methods described above have a difficulty in manufacturing electrodes with a large area.
Korean Patent Publication No. 2010-0111411 discloses an aluminum electrode paste and a solar cell using the same. According to a description thereof, the aluminum electrode paste includes three types of aluminum powder whose particle size is different from one another, glass frit, and an organic binder. The paste effectively forms a back surface field by increasing an area in contact with a silicon wafer and a diffusion area, improves electrical properties by mixing particles whose size is different from one another to increase filling density of the aluminum powder, and reducing a shrinkage factor of particles by reducing thermal expansion of metal elements in a thermal process. However, to dry the paste, the method includes a first heating with 80 to 200° C. and a second heating with 700 to 900° C., thereby causing a thermal defect of an organic layer.
Recently, there has been researched a method for improving a sputtering process in order to mass-produce large sized organic light emitting diodes. For example, there is a method for forming an aluminum cathode of an OLED without a defect of plasma by using mirror shape target sputtering (MSTS) disclosed in 19p of Applied physics letters Vol. 85 (2004). Also, there is an example of coating a substrate of 20×20 by amending the method.
However, as described above, according to the thermal evaporation method and sputtering method, there is caused excessive loss of material, is required a heavy charge for manufacturing and maintaining evaporation facilities, and is a difficulty in manufacturing large sized electrodes due to a limitation in increasing a volume of a vacuum chamber. Also, recently, there is required enlargement of not only environmental energy devices such as OLEDs and organic solar cells but also electrodes used for displays, which are seventh generation with 1870×2200 mm and eighth generation with 2200×2500 mm.
Therefore, the present invention provides a method for manufacturing an aluminum precursor solution and a method for coating using the same to manufacture an aluminum electrode using a solution process, whose electrical properties are competitive with those of aluminum electrodes manufactured by a vacuum evaporation, which is capable of being applied to a large area.